1. Field of Invention
The present invention relates generally to fuel injection assemblies for gas turbine engines.
2. Description of Related Art
There is a continuing need, driven by environmental concerns and governmental regulations, for improving the efficiency of and decreasing the emissions from gas turbine engines of the type utilized to power jet aircraft or generate electricity. Particularly, there is a continuing drive to reduce nitrous oxide (NOx) emissions.
Advanced gas turbine combustors must meet these requirements for lower NOx emissions under conditions in which the control of NOx generation is very challenging. For example, the goal for the Ultra Efficient Engine Technology (UEET) gas turbine combustor research being done by NASA is a 70 percent reduction in NOx emissions and a 15 percent improvement in fuel efficiency compared to ICAO 1996 STANDARDS TECHNOLOGY. Realization of the fuel efficiency objective will require an overall cycle pressure ratio as high as 60 to 1 and a peak cycle temperature of 3000° F. or greater. The severe combustor pressure and temperature conditions required for improved fuel efficiency make the NOx emissions goal much more difficult to achieve.
One approach to achieving low NOx emissions is via a class of fuel injectors known as lean direct injectors (LDI), such as LDI injector 10 shown in FIG. 4. Lean direct injection designs seek to rapidly mix the fuel and air to a lean stoichiometry after injection into the combustor. If the mixing occurs very rapidly, the opportunity for near stoichiometric burning is limited, resulting in low NOx production.
Conventional fuel injectors that produce low NOx emissions at high power conditions, such as LDI injector 10 shown in FIG. 4, have several disadvantages, including for example, the potential for excessive combustion dynamics or pressure fluctuations caused by combustion instability. Combustion instability occurs when the heat release couples with combustor acoustics such that random pressure perturbations in the combustor are amplified into large pressure oscillations. These large pressure oscillations, such as those pressure oscillations having amplitudes of about 1-5% of the combustor pressure, can have catastrophic consequences, and thus, must be reduced and/or eliminated.